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87 lines
2.6 KiB
JavaScript
87 lines
2.6 KiB
JavaScript
(function (exports) {
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'use strict';
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exports.longestCommonSubsequence = (function () {
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/**
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* Find the lengths of longest common sub-sequences
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* of two strings and their substrings.
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*
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* Complexity: O(MN).
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*
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* @private
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* @param {String} first string
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* @param {String} second string
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* @return {Array} two dimensional array with LCS
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* lengths of input strings and their substrings.
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*
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*/
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function getLcsLengths(str1, str2) {
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var result = [];
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for (var i = -1; i < str1.length; i = i + 1) {
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result[i] = [];
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for (var j = -1; j < str2.length; j = j + 1) {
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if (i === -1 || j === -1) {
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result[i][j] = 0;
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} else if (str1[i] === str2[j]) {
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result[i][j] = result[i - 1][j - 1] + 1;
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} else {
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result[i][j] = Math.max(result[i - 1][j], result[i][j - 1]);
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}
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}
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}
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return result;
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}
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/**
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* Find longest common sub-sequences of two strings.
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*
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* Complexity: O(M + N).
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*
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* @private
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* @param {String} first string
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* @param {String} second string
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* @return {Array} two dimensional array with LCS
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* lengths of input strings and their substrings
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* returned from 'getLcsLengths' function.
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*
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*/
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function getLcs(str1, str2, lcsLengthsMatrix) {
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var execute = function (i, j) {
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if (!lcsLengthsMatrix[i][j]) {
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return '';
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} else if (str1[i] === str2[j]) {
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return execute(i - 1, j - 1) + str1[i];
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} else if (lcsLengthsMatrix[i][j - 1] > lcsLengthsMatrix[i - 1][j]) {
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return execute(i, j - 1);
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} else {
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return execute(i - 1, j);
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}
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};
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return execute(str1.length - 1, str2.length - 1);
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}
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/**
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* Algorithm from dynamic programming. It finds the longest
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* common sub-sequence of two strings. For example for strings 'abcd'
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* and 'axxcda' the longest common sub-sequence is 'acd'.
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*
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* @example
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* var subsequence = require('path-to-algorithms/src/searching/'+
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* 'longest-common-subsequence').longestCommonSubsequence;
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* console.log(subsequence('abcd', 'axxcda'); // 'acd'
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*
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* @public
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* @module searching/longest-common-subsequence
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* @param {String} first input string.
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* @param {String} second input string.
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* @return {Array} Longest common subsequence.
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*/
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return function (str1, str2) {
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var lcsLengthsMatrix = getLcsLengths(str1, str2);
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return getLcs(str1, str2, lcsLengthsMatrix);
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};
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})();
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})(typeof window === 'undefined' ? module.exports : window);
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